Method and apparatus for the dialysis of blood

ABSTRACT

Apparatus for use in dialyzing a patient, the apparatus comprising:
         a hemodialysis catheter comprising:
           an elongated body having a proximal end and a distal end, wherein the distal end terminates in a substantially planar distal end surface;   first and second lumens extending from the proximal end of the elongated body to the distal end of the elongated body, wherein the first and second lumens terminate on the substantially planar distal end surface in first and second mouths, respectively, arranged in side-by-side configuration, and further wherein the first and second lumens are separated by a septum; and   first and second longitudinal slots formed in the distal end of the elongated body and communicating with the interiors of the first and second lumens, respectively, the first and second longitudinal slots opening on the substantially planar distal end surface;   wherein the first and second longitudinal slots each has a length and a width, relative to the dimensions of the first and second lumens and the rate of blood flow to be passed through the hemodialysis catheter, such that (i) when a given lumen is to be used for a return function, the primary blood flow will exit the mouth of that lumen, and (ii) when a given lumen is to be used for a suction function, the primary blood flow will enter the proximal end of the longitudinal slot associated with that lumen, whereby to minimize undesirable recirculation of dialyzed blood.

REFERENCE TO PENDING PRIOR PATENT APPLICATIONS

This patent application claims benefit of:

(i) pending prior U.S. Provisional Patent Application Ser. No.61/522,568, filed Aug. 11, 2011 by Adrian Ravenscroft et al. forAPPARATUS AND METHOD FOR THE DIALYSIS OF BLOOD (Attorney's Docket No.RAVENSCROFT-1 PROV); and

(ii) pending prior U.S. Provisional Patent Application Ser. No.61/638,079, filed Apr. 25, 2012 by Adrian Ravenscroft et al. for METHODAND APPARATUS FOR THE DIALYSIS OF BLOOD (Attorney's Docket No.RAVENSCROFT-2 PROV).

The two (2) above-identified patent applications are hereby incorporatedherein by reference.

FIELD OF THE INVENTION

This invention relates to the dialysis of blood in general, and moreparticularly to methods and apparatus for use in the same.

BACKGROUND OF THE INVENTION

A healthy kidney removes toxic wastes and excess water from the blood.In End Stage Renal Disease (“ESRD”), or chronic kidney failure, thekidneys progressively stop performing these essential functions over along period of time. When the kidneys fail, a patient dies within ashort period of time unless that patient receives dialysis treatment forthe rest of that patient's life or undergoes transplantation of ahealthy, normal kidney. Since relatively few kidneys are currentlyavailable for transplantation, the overwhelming majority of patientswith ESRD receive dialysis treatment.

Hemodialysis therapy is an extracorporeal (i.e., outside the body)process which removes toxins and water from a patient's blood. Ahemodialysis machine pumps blood from the patient, through a dialyzer,and then back into the patient. The dialyzer removes the toxins andwater from the blood by a membrane diffusion process. Typically, apatient with chronic kidney disease requires hemodialysis treatmentsthree times per week, for 3-6 hours per session.

Thus, hemodialysis treatments require repetitive access to the vascularsystem of the patient.

One common method for repetitively accessing the vascular system of apatient for hemodialysis involves the use of a percutaneous catheter.The percutaneous catheter is inserted into a major vein, such as afemoral, subclavian or jugular vein. For long term maintenance dialysis,a jugular vein is generally the preferred insertion site. The catheteris percutaneous, with one end external to the body and the other enddwelling in either the superior vena cava or the right atrium of theheart. The external portion of the catheter has connectors permittingattachment of blood lines leading to and from the hemodialysis machine.

FIGS. 1 and 2 show a typical prior art hemodialysis catheter 5 disposedin the body of a patient. More particularly, hemodialysis catheter 5generally comprises a catheter portion 10 comprising a dual-lumencatheter element 15, and a connector portion 20 comprising anextracorporeal connector element 25. The catheter's extracorporealconnector element 25 is disposed against the chest 30 of the patient,with the distal end 35 of catheter element 15 extending down thepatient's jugular vein 40 and into the patient's superior vena cava 45.More particularly, the distal end 35 of dual-lumen catheter element 15is positioned within the patient's superior vena cava 45 such that themouth 50 of the suction line (i.e., lumen) 55, and the mouth 60 of thereturn line (i.e., lumen) 65, are both located between the patient'sright atrium 70 and the patient's left subclavia vein 75 and rightsubclavia vein 80. Alternatively, the distal end 35 of dual-lumencatheter element 15 may be positioned so that mouth 50 of suction line55, and mouth 60 of return line 65, are located within the patient'sright atrium 70. The hemodialysis catheter 5 is then left in thisposition relative to the body, waiting to be used during an activedialysis session.

When hemodialysis is to be performed on a patient, the catheter'sextracorporeal connector element 25 is appropriately connected to adialysis machine (not shown), i.e., suction line 55 is connected to thesuction port of the dialysis machine, and return line 65 is connected tothe return port of the dialysis machine. The dialysis machine is thenactivated (i.e., the dialysis machine's blood pump is turned on and theflow rate set), whereupon the dialysis machine will withdraw relatively“dirty” blood from the patient through suction line 55 and returnrelatively “clean” blood to the patient through return line 65.

In order to minimize clotting within the hemodialysis catheter betweendialysis sessions, the lumens of the hemodialysis catheter are typicallyfilled with a diluted heparin solution (i.e., a “lock solution”) betweenthe dialysis sessions. More particularly, after a dialysis session hasbeen completed, a diluted heparin solution (i.e., the “lock solution”)is loaded into the lumens of the hemodialysis catheter and clamps set atthe proximal end of the hemodialysis catheter (i.e., at the catheter'sextracorporeal connector element 25). These clamps prevent the locksolution from draining out of the distal end of the catheter intosystemic circulation. At the start of a hemodialysis session, the clampsare released and the lock solution is withdrawn from the hemodialysiscatheter, whereupon the hemodialysis catheter is ready for use in adialysis procedure.

It will be appreciated that the efficiency of a hemodialysis procedurewill be reduced if there is recirculation of the dialyzed blood flow,i.e., if the cleansed blood returning to the body through the returnline 65 is immediately drawn back into the suction line 55. To avoidthis problem, hemodialysis catheters have traditionally staggered theopenings 50, 60 of the lines 55, 65, respectively, in the manner shownin FIG. 2, i.e., so that mouth 60 of return line 65 is disposed distalto mouth 50 of suction line 55. With this arrangement, given thedirection of the blood flow in superior vena cava 45, mouth 60 of returnline 65 is always disposed “downstream” of mouth 50 of suction line 55.As a result, there is a reduced possibility that the cleansed bloodreturning to the body through return line 65 will be immediately drawnback into suction line 55, and hence any undesirable recirculation ofthe cleansed blood flow is minimized.

One consequence of forming the hemodialysis catheter with theaforementioned “staggered tip” configuration (i.e., so that mouth 60 ofreturn line 65 is disposed distal to mouth 50 of suction line 55) isthat each lumen of the dual-lumen hemodialysis catheter is effectivelydedicated to a particular function, i.e., line 65 is limited to use as areturn line and line 55 is limited to use as a suction line. This pointbecomes clear if one considers the effect of reversing the use of eachline, i.e., of using line 65 as a suction line and of using line 55 as areturn line—in this reversed situation, the undesirable recirculation ofthe cleansed blood would tend to increase significantly, since thecleansed blood emerging from the mouth of the return line would bereleased just upstream of the mouth of the suction line, so that thecleansed blood would tend to be drawn back into the mouth of the suctionline immediately after being returned to the body. As a result, therewould be a significant reduction in the efficiency of a hemodialysisprocedure (e.g., 15-30%, depending on the catheter tip design), andhence dialysis sessions would need to increase significantly in durationand/or frequency. Furthermore, if such a line reversal were to occurinadvertently and escape the attention of the attending medicalpersonnel, the reduced hemodialysis efficiency might cause a patient tounknowingly receive inadequate dialysis during a treatment session,which could have serious health consequences for the patient.

The requirement that each line be dedicated to a particular function(i.e., suction or return, depending on whether its mouth is disposedproximal or distal to the mouth of its counterpart line) can beproblematic in certain situations.

By way of example but not limitation, if a blood clot were to form inthe suction line, it could be desirable to reverse flow through thisline to see if the blood clot could be cleared from the catheter byforcing the blood clot out the distal end of the catheter. However, thisapproach requires the aforementioned line reversal, with the suctionline being used as the return line and the return line being used as thesuction line. As noted above, such line reversal is problematic wherethe hemodialysis catheter utilizes the aforementioned “staggered tip”construction.

By way of further example but not limitation, where the disposition ofthe hemodialysis catheter within the vascular system of the patient issuch that suction from the suction line causes the hemodialysis catheterto repeatedly adhere to a vascular wall, it could be desirable toreverse flow through this line to avoid such recurrent adhesion.However, as noted above, such line reversal is problematic where thehemodialysis catheter utilizes the aforementioned “staggered tip”construction, since the mouth of the suction line should be disposedupstream of the mouth of the return line in order to minimize therecirculation of dialyzed blood.

The requirement that each line be dedicated to a particular function(i.e., suction or return, depending on whether its mouth is disposedproximal or distal to the mouth of its counterpart line) is eliminatedif the two lines of the dialysis catheter co-terminate, i.e., if themouths of the two lines are disposed in a side-by-side configuration,such as that shown in FIG. 3. This construction can be highly desirable,since it eliminates the need to dedicate a particular line to aparticular function, and hence would greatly simplify dialysis setup andprovide increased flexibility during catheter operation. However, in aconventional application of this side-by-side construction, hemodialysisefficiency is greatly reduced, since the mouth of the return line is nolonger disposed distal to the mouth of the suction line, and hence thereis a much higher likelihood that cleansed blood exiting the return linewill be immediately drawn back into the suction line of the dialysiscatheter, thereby resulting in the undesirable recirculation problemdiscussed above. Furthermore, where the mouths of the two lines aredisposed in a side-by-side configuration such as that shown in FIG. 3,suction from the suction line may cause the distal tip of thehemodialysis catheter to adhere to a vascular wall (see, for example,FIG. 4), which can also greatly reduce catheter efficiency. In order toreduce the possibility of, and/or in order to reduce the effects of,such suction adhesion to an adjacent vascular wall, some hemodialysiscatheters provide small holes in the sides of the catheter, proximal tothe catheter tip. Such side holes can permit blood flow to continue evenwhere suction causes the distal end of the catheter to adhere to anadjacent vascular wall. However, since these side holes are smaller insize than the mouth of the suction line, they are incapable ofsupporting normal catheter flow rates and hence catheter flow rates arestill greatly reduced.

Prior art hemodialysis catheters also tend to suffer from variousadditional deficiencies. By way of example but not limitation, even withthe use of catheter lock solutions between dialysis sessions, bloodclots may form in the mouths of one or both lumens of the hemodialysiscatheter, and at locations between the mouths of the two lumens. This isparticularly true during the time between dialysis sessions, when thehemodialysis catheter is not in active use. This is because the distalend of the hemodialysis catheter is disposed in a turbulent bloodenvironment, and some of the catheter lock solution inevitably leaks outof the distal end of the hemodialysis catheter and is replaced by blood,which can then clot at the distal end of the hemodialysis catheter.These blood clots can be difficult and/or time-consuming to remove,thereby slowing down dialysis set-up and/or reducing dialysisthroughput. In this respect it should be appreciated that blood clotremoval can be particularly difficult where side windows are formedadjacent to the distal ends of the lumens of the hemodialysis catheter,since portions of the blood clots may extend through the windows andthereby mechanically “lock” the blood clots to the hemodialysiscatheter.

Therefore, it would be desirable to provide a new hemodialysis catheterwhich is configured to minimize the aforementioned undesirablerecirculation of dialyzed blood, yet which allows its lumens to beinterchangeably used for suction or return functions. It would also bedesirable to provide a new hemodialysis catheter which minimizes thepossibility of the catheter inadvertently adhering to vascular walls,and which simplifies removing any clots which might form adjacent to thedistal end of the catheter. And it would be desirable to provide a newhemodialysis catheter which is easy to manufacture and inexpensive toproduce.

SUMMARY OF THE INVENTION

The present invention provides a novel method and apparatus for thedialysis of blood. Among other things, the present invention comprisesthe provision and use of a novel hemodialysis catheter which isconfigured to minimize the aforementioned undesirable recirculation ofdialyzed blood, yet which allows its lumens to be interchangeably usedfor suction or return functions. The novel hemodialysis catheter is alsodesigned to minimize the possibility of the catheter inadvertentlyadhering to vascular walls, and to simplify removal of any clots whichmight form adjacent to the distal end of the catheter. And the novelhemodialysis catheter is easy to manufacture and inexpensive to produce.

In one form of the invention, there is provided apparatus for use indialyzing a patient, the apparatus comprising:

a hemodialysis catheter comprising:

-   -   an elongated body having a proximal end and a distal end,        wherein the distal end terminates in a substantially planar        distal end surface;    -   first and second lumens extending from the proximal end of the        elongated body to the distal end of the elongated body, wherein        the first and second lumens terminate on the substantially        planar distal end surface in first and second mouths,        respectively, arranged in side-by-side configuration, and        further wherein the first and second lumens are separated by a        septum; and    -   first and second longitudinal slots formed in the distal end of        the elongated body and communicating with the interiors of the        first and second lumens, respectively, the first and second        longitudinal slots opening on the substantially planar distal        end surface;    -   wherein the first and second longitudinal slots each has a        length and a width, relative to the dimensions of the first and        second lumens and the rate of blood flow to be passed through        the hemodialysis catheter, such that (i) when a given lumen is        to be used for a return function, the primary blood flow will        exit the mouth of that lumen, and (ii) when a given lumen is to        be used for a suction function, the primary blood flow will        enter the proximal end of the longitudinal slot associated with        that lumen, whereby to minimize undesirable recirculation of        dialyzed blood.

In one preferred form of the invention, where the dialysis flow rate isbetween about 350 mL/minute and 500 mL/minute, and where the suction(vacuum) prepump pressure is not more negative than about −250 mm/Hg andthe return pressure does not exceed about 250 mm/Hg, and where thesuction line and the return line both have D-shaped cross-sections witha longer dimension of about 3.5 mm and a shorter dimension of about 1.5mm, the first and second longitudinal slots preferably have a slot widthof about 0.065-0.100 inches, and a slot length of greater than 5 mm,with a slot length of 10 mm being preferred. In this respect it shouldbe appreciated that an appropriate slot width is important to allowsufficient flow rates at acceptable pressure gradients, and anappropriate slot length is important to minimize recirculation.

In another form of the invention, there is provided apparatus for use indialyzing a patient, the apparatus comprising:

a hemodialysis catheter system comprising:

-   -   a first elongated body having a proximal end and a distal end,        wherein the distal end terminates in a first substantially        planar distal end surface;    -   a first lumen extending from the proximal end of the first        elongated body to the distal end of the first elongated body,        wherein the first lumen terminates on the first substantially        planar distal end surface in a first mouth;    -   a first longitudinal slot formed in the distal end of the first        elongated body and communicating with the interior of the first        lumen, the first longitudinal slot opening on the first        substantially planar distal end surface;    -   a second elongated body having a proximal end and a distal end,        wherein the distal end terminates in a second substantially        planar distal end surface;    -   a second lumen extending from the proximal end of the second        elongated body to the distal end of the second elongated body,        wherein the second lumen terminates on the second substantially        planar distal end surface in a second mouth;    -   a second longitudinal slot formed in the distal end of the        second elongated body and communicating with the interior of the        second lumen, the second longitudinal slot opening on the second        substantially planar distal end surface;    -   wherein the first and second longitudinal slots each has a        length and a width, relative to the dimensions of the first and        second lumens and the rate of blood flow to be passed through        the hemodialysis catheter system, such that (i) when a given        lumen is to be used for a return function, the primary blood        flow will exit the mouth of that lumen, and (ii) when a given        lumen is to be used for a suction function, the primary blood        flow will enter the proximal end of the longitudinal slot        associated with that lumen, whereby to minimize undesirable        recirculation of dialyzed blood.

In another form of the invention, there is provided a method fordialyzing the blood of a patient, the method comprising:

providing apparatus for use in dialyzing a patient, the apparatuscomprising:

-   -   a hemodialysis catheter comprising:        -   an elongated body having a proximal end and a distal end,            wherein the distal end terminates in a substantially planar            distal end surface;        -   first and second lumens extending from the proximal end of            the elongated body to the distal end of the elongated body,            wherein the first and second lumens terminate on the            substantially planar distal end surface in first and second            mouths, respectively, arranged in side-by-side            configuration, and further wherein the first and second            lumens are separated by a septum; and        -   first and second longitudinal slots formed in the distal end            of the elongated body and communicating with the interiors            of the first and second lumens, respectively, the first and            second longitudinal slots opening on the substantially            planar distal end surface;        -   wherein the first and second longitudinal slots each has a            length and a width, relative to the dimensions of the first            and second lumens and the rate of blood flow to be passed            through the hemodialysis catheter, such that (i) when a            given lumen is to be used for a return function, the primary            blood flow will exit the mouth of that lumen, and (ii) when            a given lumen is to be used for a suction function, the            primary blood flow will enter the proximal end of the            longitudinal slot associated with that lumen, whereby to            minimize undesirable recirculation of dialyzed blood;

connecting the first lumen to the venous port of a dialysis machine, andconnecting the second lumen to the arterial port of the dialysismachine; and

withdrawing undialyzed blood from the body of a patient through thefirst lumen, and returning dialyzed blood to the body of a patientthrough the second lumen.

In another form of the invention, there is provided apparatus for use inwithdrawing fluids from a patient and instilling fluids into a patient,the apparatus comprising:

a catheter comprising:

-   -   an elongated body having a proximal end and a distal end,        wherein the distal end terminates in a substantially planar        distal end surface;    -   first and second lumens extending from the proximal end of the        elongated body to the distal end of the elongated body, wherein        the first and second lumens terminate on the substantially        planar distal end surface in first and second mouths,        respectively, arranged in side-by-side configuration, and        further wherein the first and second lumens are separated by a        septum; and    -   first and second longitudinal slots formed in the distal end of        the elongated body and communicating with the interiors of the        first and second lumens, respectively, the first and second        longitudinal slots opening on the substantially planar distal        end surface;    -   wherein the first and second longitudinal slots each has a        length and a width, relative to the dimensions of the first and        second lumens and the rate of fluid flow to be passed through        the catheter, such that (i) when a given lumen is to be used for        an instilling function, the primary fluid flow will exit the        mouth of that lumen, and (ii) when a given lumen is to be used        for a suction function, the primary fluid flow will enter the        proximal end of the longitudinal slot associated with that        lumen, whereby to minimize undesirable recirculation of fluid.

In another form of the invention, there is provided apparatus for use inwithdrawing fluids from a patient and instilling fluids into a patient,the apparatus comprising:

a catheter system comprising:

-   -   a first elongated body having a proximal end and a distal end,        wherein the distal end terminates in a first substantially        planar distal end surface;    -   a first lumen extending from the proximal end of the first        elongated body to the distal end of the first elongated body,        wherein the first lumen terminates on the first substantially        planar distal end surface in a first mouth;    -   a first longitudinal slot formed in the distal end of the first        elongated body and communicating with the interior of the first        lumen, the first longitudinal slot opening on the first        substantially planar distal end surface;    -   a second elongated body having a proximal end and a distal end,        wherein the distal end terminates in a second substantially        planar distal end surface;    -   a second lumen extending from the proximal end of the second        elongated body to the distal end of the second elongated body,        wherein the second lumen terminates on the second substantially        planar distal end surface in a second mouth;    -   a second longitudinal slot formed in the distal end of the        second elongated body and communicating with the interior of the        second lumen, the second longitudinal slot opening on the second        substantially planar distal end surface;    -   wherein the first and second longitudinal slots each has a        length and a width, relative to the dimensions of the first and        second lumens and the rate of fluid flow to be passed through        the catheter system, such that (i) when a given lumen is to be        used for an instilling function, the primary fluid flow will        exit the mouth of that lumen, and (ii) when a given lumen is to        be used for a suction function, the primary fluid flow will        enter the proximal end of the longitudinal slot associated with        that lumen, whereby to minimize undesirable recirculation of        fluid.

In another form of the invention, there is provided a method forwithdrawing fluids from a patient and instilling fluids into a patient,the method comprising:

providing apparatus for use in withdrawing fluids from a patient andinstilling fluids into a patient, the apparatus comprising:

-   -   a catheter comprising:        -   an elongated body having a proximal end and a distal end,            wherein the distal end terminates in a substantially planar            distal end surface;        -   first and second lumens extending from the proximal end of            the elongated body to the distal end of the elongated body,            wherein the first and second lumens terminate on the            substantially planar distal end surface in first and second            mouths, respectively, arranged in side-by-side            configuration, and further wherein the first and second            lumens are separated by a septum; and        -   first and second longitudinal slots formed in the distal end            of the elongated body and communicating with the interiors            of the first and second lumens, respectively, the first and            second longitudinal slots opening on the substantially            planar distal end surface;        -   wherein the first and second longitudinal slots each has a            length and a width, relative to the dimensions of the first            and second lumens and the rate of fluid flow to be passed            through the catheter, such that (i) when a given lumen is to            be used for an instilling function, the primary fluid flow            will exit the mouth of that lumen, and (ii) when a given            lumen is to be used for a suction function, the primary            fluid flow will enter the proximal end of the longitudinal            slot associated with that lumen, whereby to minimize            undesirable recirculation of fluid;

connecting the first lumen to a source of suction, and connecting thesecond lumen to a source of fluid; and

withdrawing fluid from the body of a patient through the first lumen,and instilling fluid into the body of a patient through the secondlumen.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore fully disclosed or rendered obvious by the following detaileddescription of the preferred embodiments of the invention, which is tobe considered together with the accompanying drawings wherein likenumbers refer to like parts, and further wherein:

FIGS. 1 and 2 are schematic views showing one prior art hemodialysiscatheter disposed in the body of a patient;

FIG. 3 is a schematic view showing another prior art hemodialysiscatheter disposed in the body of a patient;

FIG. 4 is a schematic view showing the prior art hemodialysis catheterof FIG. 3 adhering to vascular tissue;

FIGS. 5 and 6 are schematic views showing a novel hemodialysis catheterformed in accordance with the present invention;

FIGS. 7 and 8 are schematic views (not necessarily to scale) showing thedistal end of the novel hemodialysis catheter of FIGS. 5 and 6, with theviews of FIGS. 7 and 8 being taken orthogonal to one another, and withFIG. 8 being a cross-sectional view taken along line 8-8 of FIG. 6;

FIG. 9 is a schematic view (not necessarily to scale) showing the modeof operation of the novel hemodialysis catheter of FIGS. 5-8;

FIGS. 10-16 are schematic views showing how blood flow into, and out of,the novel hemodialysis catheter of FIGS. 5 and 6 minimizesrecirculation;

FIGS. 17-25 are schematic views showing how an open/close valve may beincorporated into one or both of the blood lines of the novelhemodialysis catheter of FIGS. 5 and 6 in order to facilitate flowcontrol;

FIGS. 26-35 are schematic views showing a novel tunneling tool which maybe used in connection with the novel hemodialysis catheter of FIGS. 5and 6;

FIGS. 35A and 35B are schematic views showing another form of tunnelingtool which may be used in connection with the novel hemodialysiscatheter of FIGS. 5 and 6;

FIG. 36 is a schematic view showing two single-lumen hemodialysiscatheters also formed in accordance with the present invention;

FIGS. 37-39 are schematic views showing a novel apheresis catheter alsoformed in accordance with the present invention; and

FIG. 40 is a schematic view like that of FIG. 5, except that the twolumen hemodialysis catheter has its connector portion replaced by animplantable port.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a novel method and apparatus for thedialysis of blood. Among other things, the present invention comprisesthe provision and use of a novel hemodialysis catheter which isconfigured to minimize the aforementioned undesirable recirculation ofdialyzed blood, yet which allows its lumens to be interchangeably usedfor suction or return functions. The novel hemodialysis catheter of thepresent invention is also designed to minimize the possibility of thecatheter inadvertently adhering to vascular walls, and to simplifyremoval of any clots which might form adjacent to the distal end of thecatheter. And the novel hemodialysis catheter of the present inventionis easy to manufacture and inexpensive to produce.

More particularly, and looking now at FIGS. 5-8, there is shown a novelhemodialysis catheter 105 which is intended for use in the dialysis ofblood. Hemodialysis catheter 105 generally comprises a catheter portion110 comprising a dual-lumen catheter element 115, and a connectorportion 120 comprising an extracorporeal connector element 125. Thecatheter's extracorporeal connector element 125 is disposed against thechest 130 of the patient, with the distal end 135 of catheter element115 extending down the patient's internal jugular vein 140 and into thepatient's superior vena cava 145. More particularly, the distal end 135of dual-lumen catheter element 115 is positioned within the patient'ssuperior vena cava 145 such that the mouth 150 of a first lumen 155, andthe mouth 160 of a second lumen 165, are both located between thepatient's right atrium and the patient's left subclavia vein and rightsubclavia vein. Alternatively, the distal end 135 of dual-lumen catheterelement 115 may be positioned so that mouth 150 of first lumen 155, andmouth 160 of second lumen 165, are located within the patient's rightatrium. The hemodialysis catheter 105 is then left in this positionrelative to the body, waiting to be used during an active dialysissession.

Significantly, mouth 150 of first lumen 155 and mouth 160 of secondlumen 165 are disposed in a side-by-side configuration, with thedual-lumen catheter element 115 terminating in a substantially flatdistal end surface 175. Flat distal end surface 175 of dual-lumencatheter element 115 preferably extends substantially perpendicular tothe longitudinal axes of first lumen 155 and second lumen 165. Bydisposing mouths 150 and 160 in the aforementioned side-by-sideconfiguration, lumens 155 and 165 may be interchangeably used forsuction or return applications, as will hereinafter be discussed.

Also significantly, a pair of longitudinal slots 180, 185 are formed inthe side walls of distal end 135 of dual-lumen catheter element 115,with longitudinal slot 180 extending along and communicating with theinterior of first lumen 155, and with longitudinal slot 185 extendingalong and communicating with the interior of second lumen 165.Preferably longitudinal slots 180, 185 extend at a right angle to theplane of the septum 190 which separates first lumen 155 from secondlumen 165. By providing first lumen 155 and second lumen 165 with theaforementioned longitudinal slots 180, 185, respectively, theaforementioned undesirable recirculation of dialyzed blood is minimized,even though the mouths 150, 160 of the lumens 155, 165, respectively,are disposed in a side-by side configuration, as will hereinafter bediscussed.

In one preferred form of the present invention, the distal end 135 ofcatheter element 115 has a substantially round outer surface (i.e., thedistal end 135 of catheter element 115 has a substantially roundcross-section), and first lumen 155 and second lumen 165 are each formedwith a substantially D-shaped cross-section (FIG. 6), characterized by alonger dimension 195 and a shorter dimension 200.

When hemodialysis is to be performed on a patient, extracorporealconnector element 125 of hemodialysis catheter 105 is appropriatelyconnected to a dialysis machine (not shown), e.g., first line 155 isconnected to the suction port of the dialysis machine, and second line165 is connected to the return port of the dialysis machine. In thiscase, first line 155 serves as the suction line and second line 165serves as the return line. Alternatively, first line 155 is connected tothe return port of the dialysis machine, and second line 165 isconnected to the suction port of the dialysis machine. In this case,first line 155 serves as the return line and second line 165 serves asthe suction line. It is a significant aspect of the present inventionthat the lumens of the hemodialysis catheter 105 are not dedicated to aparticular function, i.e., either lumen may be used for suction functionand either lumen may be used for return function.

For the purposes of the description which hereinafter follows, it willbe assumed that first line 155 is connected to the suction port of thedialysis machine, and second line 165 is connected to the return port ofthe dialysis machine. In this case, first line 155 serves as the suctionline to withdraw undialyzed blood from the patient and second line 165serves as the return line to return dialyzed blood to the patient.

The dialysis machine is then activated (i.e., the dialysis machine'sblood pump is turned on and the flow rate set), whereupon the dialysismachine will withdraw relatively “dirty” blood from the patient throughsuction line 155 and return relatively “clean” blood to the patientthrough return line 165.

Significantly, with the novel hemodialysis catheter of the presentinvention, there is minimal undesirable recirculation of the undialyzedblood, even though mouth 150 of first lumen 155 (i.e., the mouth of thesuction line) is disposed immediately adjacent to mouth 160 of secondlumen 165 (i.e., the mouth of the return line) in a side-by-siderelation. This is due to the novel provision of the aforementionedlongitudinal slots 180, 185. More particularly, and looking now at FIGS.9 and 10, longitudinal slots 180, 185 are configured such that themajority of the blood taken in by suction line 155 is admitted at theproximal end of longitudinal slot 180, where the level of suction is thegreatest; and the majority of the blood discharged by return line 165 isejected at the distal end of lumen 165, i.e., out mouth 160, since thisis in direct line with the longitudinal axis of return line 165. As aresult, there is minimal undesirable recirculation of the dialyzedblood, even though the mouths 150, 160 of lumens 155, 165, respectively,are disposed in side-by-side configuration. This result is ensured byforming longitudinal slots 180, 185 with the proper configuration (i.e.,the proper length and width) relative to the dimensions of thehemodialysis catheter and the blood flow rates through the catheter.

More particularly, it has been discovered that, by controlling certainparameters of the hemodialysis system, the recirculation rate of thedual-lumen, flat-end hemodialysis catheter 105 can be minimized. Theseparameters include, but are not limited to, (i) the size of lumens 155,165; (ii) the length and width of longitudinal slots 180, 185; (iii) thethickness of the side wall of hemodialysis catheter 105 at longitudinalslots 180, 185; and (iv) the rate of flow through hemodialysis catheter105. Another factor affecting the rate of recirculation of hemodialysiscatheter 105 is the rate of flow of the ambient blood surroundinghemodialysis catheter 105.

In general, it is preferred that longitudinal slots 180, 185 be sized sothat greater than 85% of the flow out of the return line exits thedistal mouth of that line, and so that greater than 85% of the flow intothe suction line enters the proximal ⅓^(rd) of its associatedlongitudinal slot, and so that the hemodialysis catheter has arecirculation rate of less than 1%.

In general, it is also preferred that longitudinal slots 180, 185 have alength of between approximately 8 mm and 30 mm, since this length islong enough to adequately separate the inflow and outflow streams andthereby minimize recirculation, but short enough that the entire lengthof the longitudinal slots 180, 185 can fit within the right atrium ofthe heart. In addition, it has been found that by providing longitudinalslots 180, 185 with a length of between approximately 8 mm and 30 mm,the hemodialysis catheter will function with the desired minimalrecirculation rate while minimizing loss of the catheter lock solutionthrough longitudinal slots 180, 185.

In general, it is preferred that the lumens 155, 165 have a D-shapedconfiguration, and that the width of the longitudinal slots 180, 185 bebetween approximately 30% and 60% of the longer dimension 195 of theD-shaped lumen.

By way of example but not limitation, where the hemodialysis catheter105 has a diameter of 15.5 French (i.e., 0.202 inch), where its lumens155, 165 have a substantially D-shaped cross-section characterized by alonger dimension 195 of 3.5 mm (i.e., 0.14 inch) and a shorter dimension200 of 1.5 mm (i.e., 0.060 inch), and where the flow rate of each lumenis to be set at 350-450 mL per minute, it is desirable that longitudinalslots 180, 185 have a length of 10 mm (i.e., 0.394 inch) and a width of1.5 mm (i.e., 0.059 inch), whereby to produce a recirculation rate ofless than 1%.

Among other things, it should be appreciated that an appropriate slotwidth is important to allow sufficient flow rates at acceptable pressuregradients, and an appropriate slot length is important to minimizerecirculation. In this respect it will be appreciated that a wider slotand lower pressure gradients help minimize hemolysis.

FIGS. 11-16 illustrate experimental results confirming that, byproviding lumens 155, 165 with appropriately-sized longitudinal slots180, 185, recirculation can be effectively eliminated even where mouths150, 160 of lumens 155, 165 are arranged in a side-by-sideconfiguration.

In addition to the foregoing, it should also be appreciated that, eventhough the distal end of novel hemodialysis catheter 105 terminates in aflat distal end surface 175, with mouths 150 and 160 arranged in aside-by-side configuration, the construction of hemodialysis catheter105 minimizes the possibility of the catheter inadvertently adhering tovascular walls. This is also due to the provision of the aforementionedlongitudinal slots 180, 185. More particularly, with the hemodialysiscatheter of the present invention, if the flat distal end surface 175 ofthe dialysis catheter should encounter a vascular wall, the longitudinalslot associated with the suction line will admit blood into the suctionlumen, thereby keeping the distal end of the hemodialysis catheter fromsignificantly adhering to the vascular wall. This happens because“suction forces” to adhere the catheter to the vascular wall cannot bemaintained, since there are two openings (i.e., the slot opening and thedistal end opening) and these two openings are spaced from one anotherand located 90° apart.

Also, if a blood clot should form at the distal end of hemodialysiscatheter 105, e.g., during periods between dialysis sessions, theconstruction of the hemodialysis catheter makes it a simple matter toclear the blood clot from the distal end of the catheter. Moreparticularly, inasmuch as the longitudinal slots 180, 185 extend all theway to the distal end of the hemodialysis catheter, any blood clotsforming on the distal end of the hemodialysis catheter can be easilyremoved from the hemodialysis catheter by simply “blowing” the bloodclots out the distal end of the hemodialysis catheter—there is nomechanical adhesion of the blood clot to the hemodialysis catheter, asthere might be, for example, if the longitudinal slots 180, 185 werereplaced by windows, in which case a portion of the blood clot mightprotrude through the window and mechanically “lock” the blood clot tothe hemodialysis catheter.

And the hemodialysis catheter is exceedingly simple in design, making iteasy to manufacture and inexpensive to produce.

Thus it will be seen that the present invention provides a novelhemodialysis catheter which is configured to minimize undesirablerecirculation of dialyzed blood, yet which allows its lumens to beinterchangeably used for suction or return functions. And the presentinvention provides a novel hemodialysis catheter that minimizes thepossibility of the catheter inadvertently adhering to vascular walls,and which simplifies the removal of any clots which might form on thedistal end of the catheter. And the present invention provides a novelhemodialysis catheter which is easy to manufacture and inexpensive toproduce.

Blood Lines with Open/Close Valves

If desired, a novel open/close valve may be incorporated into each ofthe blood lines of novel hemodialysis catheter 105 in order tofacilitate flow control through the blood line.

More particularly, in prior art hemodialysis catheters, clamps areapplied to the suction and return lines at the proximal end of thehemodialysis catheter in order to close off flow when desired, e.g.,when the hemodialysis catheter is not connected to a dialysis machine,etc. However, these clamps are essentially hose clamps which compressthe suction and return lines of the hemodialysis catheter. This cancause damage to the suction and return lines, particularly over time.Furthermore, these clamps are bulky and present edges, which makes themuncomfortable for the patient. To this end, the present inventionprovides a novel open/closed valve which may be incorporated into eachof the blood lines of the novel hemodialysis catheter in order tofacilitate flow control through the blood line.

In one preferred form of the invention, and looking now at FIGS. 17-25,a valve 205 may be provided for each blood line 155, 165, where valve205 comprises a cylinder 210 which extends across the lumen of the bloodline. Cylinder 210 comprises a diametrically-extending through-hole 215which may be aligned with, or set transverse to, the longitudinal axisof the flow path, so as to open up flow, or close off flow,respectively, through the flow path of the blood line. A handle 220 isattached to cylinder 210 so as to permit the user to adjust therotational position of cylinder 210, and hence control flow through theblood line (preferably in either the “on” or “off” position).

Tunneling Tool

In practice, it is generally desirable to deploy a hemodialysis catheterso that the hemodialysis catheter enters a jugular vein of the patientand, furthermore, so that the hemodialysis catheter extends a distanceunder the skin before entering the jugular vein of the patient. Thisapproach allows the access end of the hemodialysis catheter to exit theskin of the patient at the chest of the patient even as the working endof the hemodialysis catheter enters a jugular vein for direct passagedown to the superior vena cava or the right atrium of the heart.

The procedure for deploying a hemodialysis catheter in this manner willnow be described, with reference being made to FIG. 26 of the figures:

1. locate the jugular vein 40 which is to be accessed;

2. make a first incision 225 into the skin near the jugular vein;

3. use the Seldinger technique to access the jugular vein, i.e., place aguidewire (not shown) into the jugular vein, and then place anintroducer sheath (not shown) over the guidewire and into the jugularvein;

4. make a second incision 230 into the skin on the chest;

5. advance the hemodialysis catheter, distal end first, through thesecond incision 230 on the chest, pass the hemodialysis catheter underthe skin and then out first incision 225 below the clavicle; and

6. insert the distal end of the hemodialysis catheter into the jugularvein by means of the guidewire and the introducer sheath.

As noted above, in the foregoing Step 5, when the hemodialysis catheteris advanced from the second incision 230 on the chest up to the firstincision 225, the hemodialysis catheter is passed distal end first, sothat the distal end of the hemodialysis catheter is ready to be passedinto the jugular vein of the patient.

In accordance with the present invention, and looking now at FIGS.27-35, a novel tunneling tool 240 is provided to facilitate advancementof the novel hemodialysis catheter 105, distal end first, under the skinof the patient.

More particularly, tunneling tool 240 generally comprises a shaft 245terminating at its distal end in a blunt end 250 and terminating at itsproximal end in a frustoconical section 255. Frustoconical section 235supports a pair of substantially parallel fingers 260. Fingers 260 arerelatively stiff, but are capable of flexing toward and away from oneanother. Fingers 260 preferably each include a plurality of projections265, with the projections 265 of one finger 260 extending toward theopposing finger 260. Fingers 260 have a length and a width such thatthey can be received in the aforementioned longitudinal slots 180, 185formed in the distal end of the hemodialysis catheter 105, when the flatdistal end surface 175 of the hemodialysis catheter 105 abutsfrustoconical section 255. A tapered sleeve 270 is slidably mounted onshaft 230. Sleeve 270 may be slid proximally along shaft 245 and overfingers 260 so as to bend fingers 260 inwardly, in a camming action,whereby to cause the fingers 260 to grip septum 190 of hemodialysiscatheter 105, and hence grip the distal end of the hemodialysiscatheter, e.g., in the manner of a collet. When the hemodialysiscatheter 105 is to be released from tunneling tool 240, tapered sleeve270 is slid distally, away from the hemodialysis catheter, whereby toallow fingers 260 to relax and thereby release the distal end of thehemodialysis catheter.

FIGS. 35A and 35B show another form of tunneling tool 240 formed inaccordance with the present invention. The construction of tunnelingtool 240 shown in FIGS. 35A and 35B is generally similar to theconstruction of the tunneling tool 240 shown in FIGS. 27-35, except thatin FIGS. 35A and 35B, each of the fingers 260 is provided with a singleprojection 265.

Single Lumen Construction

If desired, and looking now at FIG. 36, two separate single-lumenhemodialysis catheters 275 can be provided in place of hemodialysiscatheter 105, where each single-lumen hemodialysis catheter 275comprises a central lumen 280 terminating in a mouth 285, and has alongitudinal slot 290 extending proximally from mouth 285 andcommunicating with lumen 280. In this case, single-lumen hemodialysiscatheter 275 functions as one half of the complete hemodialysis catheter105. Again, longitudinal slot 290 is formed with a size (i.e., lengthand width) adequate to substantially eliminate recirculation even whenthe mouths 285 of the two single-lumen hemodialysis catheters aredisposed substantially adjacent to one another (e.g., withinapproximately 10 mm of one another).

Apheresis Catheter

In still another form of the invention, and looking now at FIGS. 37-39,there is provided an apheresis catheter 300 formed in accordance withthe present invention. Apheresis catheter 300 is characterized by threeor more lumens 305, each terminating in a mouth 310, with septums 315separating the lumens from one another. Mouths 310 are arranged in aside-by-side configuration. Each of the lumens 305 has a longitudinalslot 320 associated therewith, where each longitudinal slot has a size(i.e., length and width) such that recirculation is substantiallyeliminated even when one of the lumens is used as a suction line and oneof the lumens is used as a return line.

Use of the Novel Catheter with an Implantable Port and/or with OtherSystems that Exchange Bodily Fluids

It should be appreciated that the aforementioned two lumen hemodialysiscatheter 105, and/or the aforementioned several single-lumenhemodialysis catheters 275, and/or the aforementioned three or morelumen apheresis catheter 300 may be used in conjunction with animplantable port and/or other systems that exchange (remove and instill)bodily fluids. By way of example but not limitation, FIG. 40 shows onesuch configuration wherein the two lumen hemodialysis catheter 105 hasits connector portion 120 replaced by an implantable port 400.

Modifications of the Preferred Embodiments

It should be understood that many additional changes in the details,materials, steps and arrangements of parts, which have been hereindescribed and illustrated in order to explain the nature of the presentinvention, may be made by those skilled in the art while still remainingwithin the principles and scope of the invention.

1. Apparatus for use in dialyzing a patient, the apparatus comprising: ahemodialysis catheter comprising: an elongated body having a proximalend and a distal end, wherein the distal end terminates in asubstantially planar distal end surface; first and second lumensextending from the proximal end of the elongated body to the distal endof the elongated body, wherein the first and second lumens terminate onthe substantially planar distal end surface in first and second mouths,respectively, arranged in side-by-side configuration, and furtherwherein the first and second lumens are separated by a septum; and firstand second longitudinal slots formed in the distal end of the elongatedbody and communicating with the interiors of the first and secondlumens, respectively, the first and second longitudinal slots opening onthe substantially planar distal end surface; wherein the first andsecond longitudinal slots each has a length and a width, relative to thedimensions of the first and second lumens and the rate of blood flow tobe passed through the hemodialysis catheter, such that (i) when a givenlumen is to be used for a return function, the primary blood flow willexit the mouth of that lumen, and (ii) when a given lumen is to be usedfor a suction function, the primary blood flow will enter the proximalend of the longitudinal slot associated with that lumen, whereby tominimize undesirable recirculation of dialyzed blood.
 2. Apparatusaccording to claim 1 wherein the septum is substantially planar at thedistal end of the elongated body, and further wherein the first andsecond longitudinal slots are set substantially perpendicular to theplane of the septum.
 3. Apparatus according to claim 1 wherein the firstand second longitudinal slots are sized so that, when the first lumen isused as a suction line and the second lumen is used as a return line,greater than 85% of the flow into the suction line enters the proximal⅓^(rd) of the first longitudinal slot and greater than 85% of the flowout of the return line exits the second mouth of the second lumen. 4.Apparatus according to claim 1 wherein the first and second lumens eachhave a length of between about 8 mm and 30 mm.
 5. Apparatus according toclaim 1 wherein the outer surface of the distal end of the elongatedbody has a substantially circular shape, and further wherein the firstand second lumens each have a substantially D-shaped cross-sectioncharacterized by a longer dimension and a shorter dimension. 6.Apparatus according to claim 5 wherein the shorter dimension representsthe distance between the interior aspect of the first and secondlongitudinal slots and the corresponding outer surface of the septum. 7.Apparatus according to claim 5 wherein the width of the first and secondlongitudinal slots is between approximately 30% and 60% of the longerdimension of the D-shaped lumen.
 8. Apparatus according to claim 5wherein the distal end of the hemodialysis catheter has a diameter of15.5 French, wherein the first and second lumens have a longer dimensionof 3.5 mm and a shorter dimension of 1.5 mm, wherein the first andsecond longitudinal slots have a length of 10 mm and a width of 1.5 mm,and further wherein the rate of blood flow to be passed through thecatheter is 350-450 mL per minute.
 9. Apparatus according to claim 1further comprising a first open/close valve disposed across the firstlumen, and a second open/close valve disposed across the second lumen,whereby to control flow through the first and second lumens. 10.Apparatus according to claim 9 wherein the first open/close valvecomprises a first cylinder extending across the first lumen, the firstcylinder having a first through-hole extending therethrough, and thesecond open/close valve comprises a second cylinder extending across thesecond lumen, the second cylinder having a second through-hole extendingtherethrough.
 11. Apparatus according to claim 1 further comprising atunneling tool for drawing the distal end of the hemodialysis catheterthrough tissue.
 12. Apparatus according to claim 11 wherein thetunneling tool comprises a shaft having a distal end and a proximal end,and further wherein the proximal end comprises first and second fingersextending proximally from the shaft.
 13. Apparatus according to claim 12wherein each of the first and second fingers has a length and a widthsuch that the first finger can be accommodated in the first longitudinalslot of the hemodialysis catheter and the second finger can beaccommodated in the second longitudinal slot of the hemodialysiscatheter.
 14. Apparatus according to claim 13 wherein the tunneling toolcomprises means for selectively forcing the first and second fingersinto locking arrangement with the septum of the hemodialysis catheter.15. Apparatus according to claim 14 wherein the means for selectivelyforcing the first and second fingers into locking arrangement with theseptum of the hemodialysis catheter comprises a tapered sheath slidablymovable along the shaft.
 16. Apparatus for use in dialyzing a patient,the apparatus comprising: a hemodialysis catheter system comprising: afirst elongated body having a proximal end and a distal end, wherein thedistal end terminates in a first substantially planar distal endsurface; a first lumen extending from the proximal end of the firstelongated body to the distal end of the first elongated body, whereinthe first lumen terminates on the first substantially planar distal endsurface in a first mouth; a first longitudinal slot formed in the distalend of the first elongated body and communicating with the interior ofthe first lumen, the first longitudinal slot opening on the firstsubstantially planar distal end surface; a second elongated body havinga proximal end and a distal end, wherein the distal end terminates in asecond substantially planar distal end surface; a second lumen extendingfrom the proximal end of the second elongated body to the distal end ofthe second elongated body, wherein the second lumen terminates on thesecond substantially planar distal end surface in a second mouth; asecond longitudinal slot formed in the distal end of the secondelongated body and communicating with the interior of the second lumen,the second longitudinal slot opening on the second substantially planardistal end surface; wherein the first and second longitudinal slots eachhas a length and a width, relative to the dimensions of the first andsecond lumens and the rate of blood flow to be passed through thehemodialysis catheter system, such that (i) when a given lumen is to beused for a return function, the primary blood flow will exit the mouthof that lumen, and (ii) when a given lumen is to be used for a suctionfunction, the primary blood flow will enter the proximal end of thelongitudinal slot associated with that lumen, whereby to minimizeundesirable recirculation of dialyzed blood.
 17. Apparatus according toclaim 1 wherein the hemodialysis catheter comprises a third lumenextending from the proximal end of the elongated body to the distal endof the elongated body, wherein the third lumen terminates on thesubstantially planar distal end surface in a third mouth, arranged inside-by-side configuration with the first and second mouths of the firstand second lumens, respectively, and further wherein the first, secondand third lumens are separated by the septum; and a third longitudinalslot formed in the distal end of the elongated body and communicatingwith the interior of the third lumen, the third longitudinal slotopening on the substantially planar distal end surface. 18.-33.(canceled)
 34. Apparatus for use in withdrawing fluids from a patientand instilling fluids into a patient, the apparatus comprising: acatheter comprising: an elongated body having a proximal end and adistal end, wherein the distal end terminates in a substantially planardistal end surface; first and second lumens extending from the proximalend of the elongated body to the distal end of the elongated body,wherein the first and second lumens terminate on the substantiallyplanar distal end surface in first and second mouths, respectively,arranged in side-by-side configuration, and further wherein the firstand second lumens are separated by a septum; and first and secondlongitudinal slots formed in the distal end of the elongated body andcommunicating with the interiors of the first and second lumens,respectively, the first and second longitudinal slots opening on thesubstantially planar distal end surface; wherein the first and secondlongitudinal slots each has a length and a width, relative to thedimensions of the first and second lumens and the rate of fluid flow tobe passed through the catheter, such that (i) when a given lumen is tobe used for an instilling function, the primary fluid flow will exit themouth of that lumen, and (ii) when a given lumen is to be used for asuction function, the primary fluid flow will enter the proximal end ofthe longitudinal slot associated with that lumen, whereby to minimizeundesirable recirculation of fluid.
 35. Apparatus for use in withdrawingfluids from a patient and instilling fluids into a patient, theapparatus comprising: a catheter system comprising: a first elongatedbody having a proximal end and a distal end, wherein the distal endterminates in a first substantially planar distal end surface; a firstlumen extending from the proximal end of the first elongated body to thedistal end of the first elongated body, wherein the first lumenterminates on the first substantially planar distal end surface in afirst mouth; a first longitudinal slot formed in the distal end of thefirst elongated body and communicating with the interior of the firstlumen, the first longitudinal slot opening on the first substantiallyplanar distal end surface; a second elongated body having a proximal endand a distal end, wherein the distal end terminates in a secondsubstantially planar distal end surface; a second lumen extending fromthe proximal end of the second elongated body to the distal end of thesecond elongated body, wherein the second lumen terminates on the secondsubstantially planar distal end surface in a second mouth; a secondlongitudinal slot formed in the distal end of the second elongated bodyand communicating with the interior of the second lumen, the secondlongitudinal slot opening on the second substantially planar distal endsurface; wherein the first and second longitudinal slots each has alength and a width, relative to the dimensions of the first and secondlumens and the rate of fluid flow to be passed through the cathetersystem, such that (i) when a given lumen is to be used for an instillingfunction, the primary fluid flow will exit the mouth of that lumen, and(ii) when a given lumen is to be used for a suction function, theprimary fluid flow will enter the proximal end of the longitudinal slotassociated with that lumen, whereby to minimize undesirablerecirculation of fluid.
 36. (canceled)